This application claims the benefit of Korean Application No. 2000-68501, filed Nov. 17, 2000, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an error signal detection apparatus for an optical recording/reproducing system, and more particularly, to an error signal detection apparatus for an optical recording/reproducing system, which can detect a tangential tilt error signal and/or a radial tilt error signal with respect to a relative tilt between an objective lens and a recording medium, and/or a defocus error signal, using a main light beam used for recording an information signal on or reproducing an information signal from the recording medium.
2. Description of the Related Art
Optical pickups record an information signal on or reproduce the information signal from a recording medium, such as an optical disc seated on a turntable and rotating, while scanning the recording medium in the radial direction. However, if the rotating optical disc is tilted with respect to the optical axis, due to bending of the optical disc itself or due to an error in loading the disc, degradation of a recording/reproduction signal could occur.
When an optical pickup adopts a light source, which emits a shorter wavelength of light and an objective lens having a high numerical aperture (NA) to increase recording density, comma aberration caused by a tilt of the optical disc increases, thereby further degrading the recording/reproduction signal. Comma aberration increases as the tilt of the optical disc increases because optical aberration is proportional to xcex/(NA)3.
In an optical recording/reproducing system for high-density recording and reproduction in a recording medium, such as a digital versatile disc (DVD) and/or next generation DVD series (so-called high definition (HD)-DVD), there is a need for a tilt error signal detection apparatus for correcting a record/reproduction signal according to a relative tilt between the recording medium and the objective lens.
To accurately detect a radial tilt error signal, there is a need for the tilt error signal detection apparatus in the optical recording/reproducing system to detect a radial tilt error signal without being influenced by a tangential tilt, a defocus, or a detrack. To accurately detect a tangential tilt error signal, there is a need for the tilt error signal detection apparatus for in the optical recording/reproduction system to detect a tangential tilt error signal without being affected by the radial tilt, the defocus, or the detrack.
On the other hand, as shown in FIG. 1, a light beam reflected by a recording medium 10, after being focused as a light spot on the recording medium 10, is diffracted into a 0th order diffracted beam and xc2x11st order diffracted beams by, for example, pits (P) formed on the recording medium 10. Thus, a photodetector 9 in the optical pickup to detect an information signal receives the 0th order diffracted beam and the xc2x11st order diffracted beams. For the 0th order diffracted beam and xc2x11st order diffracted beams received by the photodetector 9, the 0th order diffracted beam overlaps each of the xc2x11st order diffracted beams that do not overlap each other. Detection signals from the overlapping portions between the 0th order diffracted beam and each of the xc2x11st order diffracted beams, and a detection signal from a pure 0th order diffracted beam have different phase characteristics. That is, the phase characteristics of individual light beam portions reflected/diffracted by the recording medium 10 differ from one to another. The phase characteristics of the detection signals vary according to a degree of tangential and/or radial tilt.
In a conventional error signal detection apparatus for detecting a tangential or radial tilt, a light beam reflected by the recording medium 10 is received as four divided light beams by the photodetector 9, which is divided into four sections. The four divided light beams are photoelectrically converted, separately, and the detection signals from the four divided light beams are summed or subtracted to detect a tangential or radial tilt error signal. Thus, the original phase characteristic according to position in the light beam, which is reflected/diffracted from the recording medium 10, cannot be reflected sufficiently in detecting a tangential or radial tilt error signal. As a result, the tangential or radial tilt error signal cannot be accurately detected.
On the other hand, when defocus occurs in recording data in the next generation DVD series recording medium for high-density recording, a method for compensating for defocus is needed because the high-density recording medium is greatly affected by the defocus compared to a conventional recording medium, which uses a red laser beam. In other words, when a short-wavelength light source, for example, having a blue wavelength of 420 nm or less, and an objective lens having an NA of 0.6 or more are used for high-density recording, a defocus margin becomes smaller due to a small focus depth of an incident light beam. As a result, even if a small degree of defocus occurs in the recording data, the problem of the defocus can be serious for the high-density recording medium.
As well known, when recording is performed on the DVD series recording medium, defocus may be controlled with a variation of about 230 nm by using a 650-nm light beam and an objective lens having an NA of 0.6. However, when recording is performed on the next generation DVD series recording medium using a blue light and an objective lens having, for example, an NA of 0.85, there is a need to accurately control the defocus to be within the range of tens of nanometers.
To precisely control the defocus to be within the range of tens of nanometers for data recording on the next generation DVD series recording medium, there is a need to detect a defocus error signal without being affected by detrack, and a relative tangential and radial tilt between the objective lens and the recording medium.
Various objects and advantages of the invention will be set forth in part in the description that follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To solve the above and other problems, it is an object of the present invention to provide an error signal detection apparatus for an optical recording/reproducing system, which can accurately detect a tangential tilt error signal in consideration of phase characteristics of light beam portions reflected/diffracted from an information stream of a recording medium, without being affected by radial tilt, defocus, and detrack.
It is another object of the present invention to provide an error signal detection apparatus for an optical recording/reproducing system, which can accurately detect a radial tilt error signal in consideration of phase characteristics of light beam portions reflected/diffracted from an information stream of a recording medium, without being affected by tangential tilt, defocus, and detrack.
It is another object of the present invention to provide an error signal detection apparatus for an optical recording/reproducing system, which can accurately detect a defocus error signal in consideration of phase characteristics of light beam portions reflected/diffracted from an information stream of a recording medium, without being affected by tangential and radial tilt, and detrack.
To achieve these and other objects of the present invention, there is provided an error signal detection apparatus for an optical recording/reproducing system including a light source emitting a light beam and an objective lens focusing the light beam to form a light spot on a recording medium, the apparatus including: a photodetecting unit dividing at least a part of the light beam passed through the objective lens after being reflected/diffracted from an information stream of the recording medium into light beam portions, and detecting the light beam portions; and a signal processor detecting phase differences between detection signals from the light beam portions to detect a tangential error signal.
The photodetecting unit divides the light beam into first, second, third, and fourth light beam portions in a direction corresponding to a radial direction of the recording medium, and detects and outputs first, second, fourth, and third detection signals from the first, second, third, and fourth light beam portions, and the signal processor detects and outputs the tangential tilt error signal as a sum of a phase difference between the first and second detection signals and a phase difference between the third and fourth detection signals.
The photodetecting unit divides a part of the light beam with respect to an axis crossing an optical axis parallel to a tangential direction of the recording medium, and detects therefrom first, second, third, and fourth light beam portions in directions corresponding to the radial and tangential directions of the recording medium, where the first, second, third, and fourth light beam portions are arranged in order, counterclockwise or clockwise in a 2xc3x972 matrix and where a row and a column of the matrix are parallel to directions corresponding to the radial and tangential directions of the recording medium, respectively, and the signal processor detects and outputs the tangential tilt error signal as a sum of a phase difference between the first and second detection signals corresponding to the first and third light beam portions, respectively, and a phase difference between third and fourth detection signals corresponding to the second and fourth light beam portions, respectively.
To achieve another object of the present invention, there is provided an error signal detection apparatus for an optical recording/reproducing system including a light source emitting a light beam and an objective lens focusing the light beam to form a light spot on a recording medium, the apparatus including: a photodetecting unit dividing at least a part of the light beam passed through the objective lens after being reflected/diffracted from an information stream of the recording medium into light beam portions, and detecting the light beam portions; and a signal processor detecting phase differences between detection signals from the light beam portions to detect a defocus error signal.
The photodetecting unit divides the light beam and detects therefrom first, second, third, and fourth inner portions arranged counterclockwise or clockwise in directions corresponding to radial and tangential directions of the recording medium, and into first, second, third, and fourth outer portions which are outward from the first, second, third, and fourth inner portions in a direction corresponding to the tangential direction of the recording medium, wherein the first, second, third, and fourth outer and inner portions are arranged in a 4xc3x972 matrix, where a row and a column of the matrix are parallel to directions corresponding to the radial and tangential directions of the recording medium, and the first inner and outer portions are arranged in a column different from the fourth inner and outer portions, and where a sum of the detection signals from the first outer portion and the fourth inner portion is a first detection signal, a sum of the detection signals from the fourth outer portion and the first inner portion is a second detection signal, a sum of the detection signals from the second inner portion and the third outer portion is a third detection signal, and a sum of the detection signals from the third inner portion and the second outer portion is a fourth detection signal, and the signal processor detects the radial tilt error signal as a sum of a phase difference between the first and second detection signals, and a phase difference between the third and fourth detection signals.
The above and other object of the present invention are also achieved by an error signal detection apparatus for an optical recording/reproducing system including a light source emitting a light beam and an objective lens focusing the light beam to form a light spot on a recording medium, the apparatus including: a photodetecting unit dividing at least a part of the light beam passed through the objective lens after being reflected/diffracted from an information stream of the recording medium into light beam portions, and detecting the light beam portions; and a signal processor detecting phase differences between detection signals from the light beam portions to detect a radial tilt error signal.
In one embodiment of the error signal detection apparatus, the first, second, third, and fourth outer light beam portions form a 2xc3x972 matrix, wherein a row and a column of the matrix are parallel to directions corresponding to the radial and tangential directions of the recording medium, and the first and fourth outer light beam portions are in different columns; and the signal processor receives first, second, third, and fourth outer light beam portions and processes therefrom the first, second, fourth, and third detection signals. In this case, it is preferable that, when the light beam is divided into a first outer portion, an intermediate light beam portion, and a second outer portion in a direction corresponding to the radial direction, the photodetecting unit divides the first and second outer portions of the light beam into first through fourth light beam portions, and detects the first through fourth light beam portions. Further, the light beam is divided into a first outer portion, an intermediate portion, and a second outer portion in a direction corresponding to the radial direction of the recording medium, the photodetecting unit divides the intermediate portion of the light beam and detects therefrom first, second, third, and fourth light beam portions. The photodetecting unit divides the light beam and detects therefrom the first through fourth light beam portions.
In another embodiment of the error signal detection apparatus, the photodetecting unit divides the light beam into a first outer portion, an intermediate portion, and a second outer portion in a direction corresponding to a tangential direction of the recording medium, and divides the first and second outer portions and detects therefrom first, second, third, and fourth outer light beam portions in the direction corresponding to the tangential direction of the recording medium, and arranged counterclockwise or clockwise in order, and/or divides the intermediate portion and detects therefrom first, second, third, and fourth inner light beam portions in directions corresponding to a radial direction and the tangential direction of the recording medium, where the first, second, third, and fourth outer light beam portions are arranged counterclockwise or clockwise, in order. The signal processor detects the defocus error signal as a sum of a phase difference between a first detection signal from the first outer light beam portion and/or the second inner light beam portion and a second detection signal from the second outer light beam portion and/or the first inner light beam portion, and a phase difference between a third detection signal from the third inner light beam portion and/or the fourth outer light beam portion and a fourth detection signal from the third outer light beam portion and/or the fourth inner light beam portion.
In this case, the first, second, third, and fourth outer light beam portions form a 2xc3x972 matrix, wherein a row and a column of the matrix are parallel to directions corresponding to the radial and tangential directions of the recording medium, and the first and fourth outer light beam portions are in different columns; and the signal processor receives first, second, third, and fourth outer light beam portions and processes therefrom the first, second, fourth, and third detection signals.
The first, second, third, and fourth inner light beam portions form a 2xc3x972 matrix, wherein a row and a column of the matrix are parallel to directions corresponding to the radial and tangential directions of the recording medium, and the first and fourth inner light beam portions are in different columns; and the signal processor receives first, second, third, and fourth inner light beam portions and processes therefrom the first, second, fourth, and third detection signals.
The photodetecting unit divides the first and second outer portions of the light beam and detects therefrom the first, second, third, and fourth outer light beam portions arranged counterclockwise or clockwise, in order, parallel to a direction corresponding to the tangential direction of the recording medium, and divides the intermediate portion and detects therefrom the first, second, third, and fourth inner light beam portions arranged counterclockwise or clockwise, in order, parallel to directions corresponding to the radial and tangential directions of the recording medium, wherein the first, second, third, and fourth outer and inner portions are arranged in a 4xc3x972 matrix, where a row and a column of the matrix are parallel to directions corresponding to the radial and tangential directions of the recording medium, and the first and second outer portions are located in different columns, and the signal processor outputs the sum of the phase difference between the first detection signal, which is a sum of the detection signals from the first outer light beam portion and the second inner light beam portion, and the second detection signal, which is a sum of the detection signals from the second outer light beam portion and the first inner light beam portion, and the phase difference between the third detection signal, which is a sum of detection signals from the third inner light beam portion and the fourth outer light beam portion, and the fourth detection signal, which is a sum of the detection signals from the third outer light beam portion and the fourth inner light beam portion.
In still another embodiment of the error signal detection apparatus, the photodetecting unit divides the light beam into first, second, third, and fourth light beam portions in a direction corresponding to a tangential direction of the recording medium, and detects and outputs first, second, fourth, and third detection signals from the first, second, third, and fourth light beam portions, and the signal processor detects and outputs the defocus error signal as a sum of a phase difference between the first and second detection signals and a phase difference between the third and fourth detection signals.
An error signal detection apparatus for an optical recording/reproducing system including a light source emitting a light beam and an objective lens focusing the light beam to form a light spot on a recording medium, the apparatus including: a photodetecting unit dividing at least a part of the light beam passed through the objective lens after being reflected/diffracted from an information stream of the recording medium into light beam portions and detecting the light beam portions; and a signal processor detecting phase differences between detection signals from the light beam portions to simultaneously detect two or more error signals, wherein the error signals include a tangential error signal, a defocus error signal, and a radial tilt error signal.
These together with other objects and advantages, which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.